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arXiv · 2303.01098

Determination of Molecular Energies via Quantum Imaginary Time Evolution in a Superconducting Qubit System

Zhiwen Zong·Sainan Huai·Tianqi Cai·Wenyan Jin·Ze Zhan·Zhenxing Zhang·Kunliang Bu·Liyang Sui·Ying Fei·Yicong Zheng·Shengyu Zhang·Jianlan Wu·Yi Yin
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Abstract

As a valid tool for solving ground state problems, imaginary time evolution (ITE) is widely used in physical and chemical simulations. Different ITE-based algorithms in their quantum counterpart have recently been proposed and applied to some real systems. We experimentally realize the variational-based quantum imaginary time evolution (QITE) algorithm to simulate the ground state energy of hydrogen (H2) and lithium hydride (LiH) molecules in a superconducting qubit system. The H2 molecule is directly simulated using the 3-qubit circuit with unitary-coupled clusters (UCC) ansatz. We also combine QITE with the cluster mean-field (CMF) method to obtain an effective Hamiltonian. The LiH molecule is correspondingly simulated using the 3-qubit circuit with hardware-efficient ansatz. For comparison, the LiH molecule is also directly simulated using the 4-qubit circuit with UCC ansatz at the equilibrium point. All the experimental results show a convergence within 4 iterations, with high-fidelity ground state energy obtained. For a more complex system in the future, the CMF may allow further grouping of interactions to obtain an effective Hamiltonian, then the hybrid QITE algorithm can possibly simulate a relatively large-scale system with fewer qubits.

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Zhiwen Zong, Sainan Huai, Tianqi Cai, Wenyan Jin, Ze Zhan, Zhenxing Zhang, Kunliang Bu, Liyang Sui, Ying Fei, Yicong Zheng, Shengyu Zhang, Jianlan Wu, Yi Yin. 2023-03-02. Determination of Molecular Energies via Quantum Imaginary Time Evolution in a Superconducting Qubit System. https://doi.org/10.1007/s11433-023-2315-0

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